US2299411A - Catalyzed hydrobromination of unsaturated organic compounds - Google Patents

Description

Patented on. 20, 1 942 CATALYZED HYDROBROMINATION OF UN- SATURATED ORGANIC COMPOUNDS William E. Vaughan, Berkeley, Calif., assignors to Shell Develop- Fredericlr Rust and ment Company, San

ration of Delaware Francisco, Calif., a corpo- No Drawing. 4 Application August 25, 1941,

Serial No. 408,212

9 Claims. This invention relates to an improved process for the hydrobromination of unsaturated organic compounds, and more particularly to improvev ments in the method of controlling the addition of hydrogen bromide to unsymmetrical organic compounds containing at least one olefinic or acetylenic linkage to produce addition products of a predetermined character.

It is known that hydrogen halides may be added to unsaturated hydrocarbons and to various unsaturated derivatives thereof. In fact, in 1870 Markownikofi stated that if an metrical hydrocarbon combines with a halogen acid, the halogen adds to the carbon atom with fewer hydrogen atoms, i. e. to the carbon atom which is more'under the influence of other car'- bon atoms. The same investigator further determined that when a hydrogen halide is added to a halogenated unsaturated compound such as vinyl chloride or a chlorinated propylene (i. e. to unsaturated hydrocarbons wherein one of the unsaturated carbon atoms carries a halogen atom, or wherein these unsaturated carbon atoms contain dissimilar numbers of halogen atoms directly attached thereto), the halogen atom of the hydrogen halide will add to the double bonded (unsaturated) carbon atom which carries the greater number of halogen atoms, while the hydrogen atom of the hydrogen halide molecule attaches to the adjacent unsaturated carbon atom. The above type of hydrohalogenation is termed "normal to distinguish it from the abnormal addition of a hydrogen halide, in which the hydrogen and halogen atoms are added in positions which are interchanged with respect to addition according to the above-outlined Markownikoff rule.

Various methods have been proposed for controlling the described hydrohalogenation reaction so as to form reaction products in which the hydrogen halide has been added contrary to the above Markownikofi rule. For instance, it has been proposed to effect the hydrohalogenation reaction in the presence of various peroxides, such as hydrogen peroxide, acetyl peroxide,

hydes and metal alkyls which tend to initiate I the reaction chains.

It is known that the presence of peroxide: or

of peroxide-forming compounds in unsaturated organic compounds, e. g. unsaturated hydrocarbons, is undesirable. For example, organic peroxides, when present even in relatively small concentrations, tend to catalyze the polymerization of a large number of and particularly diolefins. As to the abnormal addition ofhydrogen bromide to unsaturates by effecting the reaction under the deliberate infiuence of light, and particularly of ultra-violet radiations having wave-lengths of below about 2900 to 3000 Angstrom units, such processes necessitate the use of special equipment, such as reaction vessels provided with or containing lamps made of quartz Or other suitable materials, e. g. calcium fluoride, capable of transmitting rays of the defined wave-length, or reactionvessels consisting of such materials or containing openings or windows made of such material.

It has now been discovered that'unsaturated organic compounds of the class more fully described hereinbelow may be reacted with hydrogen bromide to effect directional addition thereof via the so-called abnormal addition, 1. e. contrary to the course stated or suggested by Markownikofl, this reaction being eifected in the absence of the undesirable peroxides or peroxideforming compounds, and without the necessity of employing any special equipment or apparaascaridole, and the like, as well as of compounds of the type of oxygen, air or ozone, all of which tend to form peroxides when contacted with unsaturated hydrocarbons. Also, it has been found that hydrogen bromide may be added to the unsaturated organic compounds in a manner contrary to Markownikofis rule by efl'ecting the reaction under the deliberate influence of ultraviolet. radiations in the presence or absence of sensitizers of the class of certain 'ketones, alderespect to the carbonyl group.

'which affect the direction of tus which was heretofore necessary when the reactions were effected under conditions requiring irradiation of the reactants. According to the present process, such abnormal addition of the hydrogen bromide to the unsaturated organic compounds is attained by effecting the reaction in the presence of ketones containing a bromine atom on the carbon atom in alpha position with These bromoketones apparently act as sensitizers to initiate the reaction mechanism, and also as compounds addition of the bromine atoms to the unsaturates treated. For example, as shown in the examples, when hydrogen bromide is mixed with propylene, and when the addition reaction is not controlled by any means, such as the addition of peroxides or the use of ultra-violet radiations, uct predominates in, or even isopropyl bromide.

dition of even small e. g. bromo-acetone;

the reaction prodconsists solely of On the other hand, the adquantities of a bromoketone, efiects a directional control unsaturated hydrocarbons,

to about 'mal temperatures of Y none, alpha-bromo-cyclohexanone,

wherein R denotes any organic radical.

' may be treated according to the hexadienel',5, hexadiene-l,4,

. may be substituted in of substantially pure n-propyl bromide. The bromoketones promote the of the hydrogen bromide eyen when the reaction thereof with the unsaturated organic compounds is efiected in the dark tures, i. e. in the neighborhood of about 25 C. C., or even at considerably lower The advantages of the present previously known processes of temperatures. process over the abnormal. addition of be readily apparent to those skilled in the art, it being noted that the process does not require any special equipment, or the use of elevated temperatures, a d does not result in the presence of undesirable peroxides in the reactants and/or reaction products.

The compounds which, according to the proces of the invention, promote'the abnormal hydrobromination of the unsaturates even when the reaction is efiected in the dark and at norabout C. or even at lower temperatures, are me a bromine atom atom in alpha position with respect to thecarbonyl group. The bromoketones may contain alkyl, aryl or aralkyl radicals attached to the carbonyl group. The following is a list of representative hydrobromination-promoting bromoketones: broino-acetone, alpha-bromo-acetophealpha-alphadibromo-acetone, alpha-alpha-dibromo-acetone, 3-bromo-butanone-2, 1-bromo-butanone-2, 1- phenyl-l-bromo-acetone, alpha-bromo-acetoacetic acid and the like, and their homologues.

Although there is no intention of. being limited by any theory of the case, it is believed at the present time that the abnormal hydrobromination reaction occurs with the following or some similar reaction chain mechanism which is initiated by the reaction of the the hydrogen bromide:

bromo-ketones with The quantity of the bromoketone or mixture of bromoketones to be added to the reactants may vary within relatively wide limits, it being understood that the amount should be suflicient to initiate and maintain the reaction chain mechanism.

The unsaturated organic compounds which process of this invention include hydrocarbons containing one or more oleflnic and/or acetylenic linkages. Examples of propylene, tone-1, pentene-2, hexene-i, 4-methyl-pentene-1, 4,4-dimethyl-pentene-1, d-methyl-pentene-z, octene-i, decene-l, cetene-l, styrene, cyclohexene,

and at normal tempera,

hydrogen bromide will such hydrocarbons are ethylene,' butene-l, butene-2, isobutylene, pen-.

"abnormal addition pounds which may be reacted with hydrogen bromoketones contain- 1 directly linked to the carbon drogen atoms attached unsaturates may contain one or'more halos atoms attached to saturated and/or unsaturated carbon atoms. Representative examples of these compounds are: vinyl halides, allyl halides, crotyl halides, methallyl halides, and the like Other examples of substituted unsaturated hydrocarbons are methyl acrylate, methyl methacrylate, divinyl ether, diallyl ether, dimethallyl ether, and the like.

A particularly suitable group of organic .com-

bromide via abnormal addition comprises the compounds, and particularly the hydrocarbons, in which the unsaturated linkage is in the terminal or alpha posit'on. Also, aliphatic hydrocarbons and their various substituted derivatives, e. g. halo-substituted derivatives, containing unsaturated linkages both in alpha and omega positions (1. e. terminal positions) may be readily hydrobrominated via abnormal addition to produce compounds in which both terminal carbon atoms have bromine atoms attached thereto. Another group of organic compounds which may be emplayed as the primary material comprises or includes organic compounds wherein an oleflnic linkage is in non-terminal carbon atoms having a dissimilar number of hyto'each of said unsatu rated carbon atoms due, for example, to various substituents attached thereto. For instance, the double bond may be between two carbon atoms which are of secondary and tertiary character, respectively. Another example is a compound in which the unsaturated carbon atoms are both primary or bothsecondary, numbers of halogen atoms, such as chlorine, bromine, fluorine and/or iodine atoms, attached to them.

The abnormal addition of the hydrogen bromide to the above-defined class of unsaturated organic liquid phase,

' system. Generally, no heating of the reactants is time suillcient to permit 3 methyl cyclohexene, 1,4 diphenyl butene-2,

1,3, pentadiene 1,4, acetylena'propyne, butyne-l, pentyne-2, heme-1,, cetyne-l, cotylacetylene. phenyl-acetylene. and the like. The above compounds, and theirvarious homologues, the nucleus and/or in the degrees. For instance, the

butadiene 1,3, pentadiene substituents in various necessary. In fact, in many instances the re-; action, although it'may be realized in the vapor phase and at temperatures of above 25 C., is preferably eii'ected in the liquid phase and at temperatures which are evenvbelow 0 C. The

reaction temperature, however, should not be below that at which the unsaturated hydrocarbon treated or the specific bromo-ketone employed becomes congealed. It was also found that the abnormal addition according to the present process, when-the reaction'is efiected in the presence of the bromoketones, proceeds regardless of the presence or absence of a liquid phase or film in the reaction zone.

' The reaction may be effected in a batch, intermittent or continuous manner. When the proctogether with a suitable amount of the bromoketone, may be conveyed under any desirable or optimum pressure and temperature into a suitable container, and then allowed to stand tor a period of the desirable or optimum Although the reactants may be kept in the-dark, it is frequently possible to' subject the. reactants'to the simultaneous action of light and ofthe bromoketones, such a procedure increasing the rate of conversion to the desired products. l

The following examples, which are to be construed as illustrative only, represent a specific embodiment of the invention. It is to be underdegree of conversion.

position between two 7 but have unequal tative, the reaction stood, howeverrthat thereis no intention oi being hydrogen bromide to propylene, the step oi by any details set iorth. adding to the reaction mass a bromoketone hav- Emma I ing a bromine atom on the carbon atom in alpha Propylene and hydrogen bromide were introduced together with bromoacetone into a pm: glass reactor in a liquid state and at a temperature oi about -'78 0., the volumetric ratio oi the three compounds in the reactor being 17:9.5:1. The reaction vessel was then sealed and allowed to stand ior a period oi about ten minutes while completely shielded even irom difl'used light.

4 During this period oi time the temperature within thereactor gradually rose to about 20 C. The reactor was then cooled by the use oi solid carbon dioxide, the product removed from the vessel. washed with caustic soda solution and water, dried, and distilled, An analysis oi the product obtained showed a substantially quantitative conversion to n-propyl bromide (i. e. product of abnormal addition). This reaction product had an index oi refraction 19% equal to 1.4340, while that of pure n-propyl bromide is 1.4341.

trample II Approximately 4.4 cc. of butene-l, about 3.2 cc. of hydrogen bromide and 0.1 cc. oi bromoacetone were mixed ior a period oi ilve minutes. The reaction product was then worked up as in the previous example. The yield was again substantially quantiproduct being substantially pure n-butyl bromide having an index oi refraction n= l.44-(the theoretical being n Example 11! Propylene and hydrogen bromide were reacted under substantially the same conditions as those employed in ExampleI, with the exception that the reaction time was lengthened to two hours and that acetone was employed in lieu of the bromo-acetone. As in the previous experiments,

the reaction was eiiected in the substantial absence oi light. The reaction product consisted solely of isopropyl bromide, i. e. product oi the normal addition of the hydrogen bromide. This showed that ketones, when used alone, do not promote the abnormal addition which is realized by the use oi the bromok'etones.

We claim as our invention:

1. In a process ioreflecting abnormal addition oi hydrogen bromide to propylene, the steps of adding bromo-acetone to the reaction mass, and eiiecting the reaction in the dark and at a temperature not in excess 01' about 25' C.

2. In a process for effecting abnormal addition together and kept in the dark a carbon atom in the carbonyl group.

stitution derivatives,

positionwith respect to the carbonyl group.

3. In a process ior eiiecting abnormal addition oi hydrogen bromide to butene-l, the steps oi adding bromo-acetone to the reaction mass, and eiiecting the reaction in the dark and perature not in excess or about 25? C.

4. In a process for efiecting abnormal addition of hydrogen bromide to butene-l, the step of adding to the reaction mass at bromoketone having a bromine atom on the carbon atom in alpha position with respect to the carbonyl group.

5. In a process oi effecting an abnormal hydrobromination' by the additionoi hydrogen bromide to an aliphatic hydrocarbon containing an alpha carbonyl group. 7. In a process of effecting abnormal hydrobromination, the step oi reacting a hydrogen bromide with an organic compound unsaturated in alpha position in the presence oi a bromoketone havinga bromine atom on a carbon atom in alpha position with respect to the carbonyl 8. The process according to claim 7, wherein the reaction is effected in the dark and at a temperature not in excess oi about 25 C. 9. In a process of eiiecting abnormal addition of hydrogen bromide, the step oi reacting hydrogen bromide with a compound selected irom the group consisting oi unsaturated hydrocarbons containing at least one oleflniclinkage in asymmetrical position in the molecule, their halo-sub- .and symmetrical unsaturated aliphatic and alicyclic hydrocarbons containing a halogen atom attached directly to only one oi the unsaturated carbon atoms in the presence oi a bromoketone having a bromine atom on pha FREDERICK RUST. WILLIAM E. VAUGHAN.

at a temposition with r spect to